, 1887-06-29

eartn s axis is mcnnod from the upright line
at an angle of 23} degrees. This simple fact
has many remarkable consequences, but be-
fore speaking OF them let US see what the
other lines in the diagram mean. I have al
ready said that the line n. S.. represents the
earth's axis. It therefore goes through the
earth from pole to pole. None of the other
lines crossing the circle mean lines going
through the globe, but they stand for lines
going rOwnd it, and you must therefore think
of them as rising from the paper at one side,
forming q half-circle and going down to
the paper at the other. The line E. 0. stands
for the equator, and since the equator has
a fixed relation to the poles, being half way
between them, it follows that when the North
pole is brought forward 23} degrees the equa-
tor Is thrust southwards to the same amount,
hence the equator is now 233 degrees south
of the suns position, or, which is the same
thing, the SUMS 231 degrees northof the equa-
tor. This is the farthestnorth he will go, and
as he then turns, the line where this happens
is called a tropic, from q Greek word mean
ing to turn, and this particular one, the North
ern tropic, is called the tropic of Can
eer. Why? Because the sun at this Itime
OF the year appears to be passing through g.
group of stars, or constellation, in the heavens,
called Cancer, from a fancied resemblance of
the figure made by the stars to the outlines of
a crab, Cancer being the Latin word for crab.
There IS a line further north marked A. c.;
it is the line which ~encloses all the district
where the sun just now is continually shin
ing. inside that circle, which of course is
234 degrees from the North Pole, the sun does
not set at present, and the nearer we go to
the pole the longer he will be before he sets.
If there were any people living at the Pole
itself they would see the sun shining for
three months yet, just as they would have
seen him shining for three months already, so
that the North Poleisnow in the middle OF It's
long day, a day lasting for six months. The
line A. c.. is called the Arctic circle, because
it lies under, or has overhead, a group of stars
called the Arctos major, which means, the
greater bear. (Another group nearer the Pole
is called the Lesser Bear.) There are two
lines south of the equator yet to be explained.
To see what they mean let US imagine that
the earth has gone round to the opposite side
of the sun, which of course it will do in six
months time, then it is plain that the
light would be falling on the earth from the
opposite side, and the sun would be shining
over the southern tropic just as he is now
shining over the northern tropic, andhe would
be shining over an area around the south pole
precisely the size of that which he now illu-
inmates constantly around the north pole.
The line An. G. enclosing this space is called
the Antartic Circle, because opposite to the
Arctic; and the southern tropic (the line 7.
Cp.) is called the tropic of Capricorn, be-
cause when the sun is over it he is passing
through a group of stars called Capricornus,
which means, the goat.
We understand now, I hope, the meaning
of the diagram, and may go on to consider
some of the remarkable consequences of the
sloping position of the earth's axis, as they
appear when the sun is at his farthest north.
First let US notice it's effect on the duration
of daylight on different parts of the earth's
surface. Look at the diagram and you will
notice that the upright line which separates
the dark from the light half of the earth's
surface, night from day, divides the equator
into equal parts, SO that the people living at
the equator, the inhabitants of the city of
Quito for instance, have now, as they always
have, the sam amount of daylight as of dark.
ness. But if we take any line north of the
equator, the Tropic of Cancer, for instance,
then we see that the upright line 40 longer
divides it into two equal parts, but divides
it so as to- leave much more in the light half
than in the dark, in other words the people
living along that line will have their days
longer than their nights. Santa Cruz lies at
about three quarters of the way from the
equator to the northern tropic, and you
know that we have long days now, the sun
rising at IS minutes after 5 o'clock in the
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